Quantum cascade laser device

ABSTRACT

A quantum cascade laser device includes a QCL element; a lens; and a lens holder having a small-diameter hole, a large-diameter hole, and a counterbore surface. At least a part of a side surface of the lens is fixed to an inner surface of the large-diameter hole in a state where an edge portion of an incident surface of the lens is in contact with the counterbore surface. A central axis of the small-diameter hole is eccentric from that of the large-diameter hole. The side surface of the lens is positioned with respect to the inner surface of the large-diameter hole along a direction from the central axis of the large-diameter hole toward the central axis of the small-diameter hole. A central axis of the lens is disposed at a position closer to the central axis of the small-diameter hole than to the central axis of the large-diameter hole.

TECHNICAL FIELD

The present disclosure relates to a quantum cascade laser device.

BACKGROUND ART

In the related art, a semiconductor laser device (semiconductor lasermodule) that accommodates a semiconductor laser element in a package hasbeen known (for example, Patent Document 1). Patent Document 1 disclosesa configuration in which a package accommodates a semiconductor laserelement and a lens holder that accommodates a lens for collimating laserlight emitted from the semiconductor laser element.

CITATION LIST Patent Document

-   Patent Document 1: Japanese Unexamined Patent Publication No.    2003-315633

SUMMARY OF INVENTION Technical Problem

Here, the beam radiation angle of laser light emitted from a quantumcascade laser element that is one type of semiconductor laser element isrelatively large. In addition, in order to reduce the size of thepackage, reducing the size of the lens accommodated in the package isrequired. For this reason, when the quantum cascade laser element isused as the semiconductor laser element, in order to concentrate thelaser light from the quantum cascade laser element having a largeradiation angle using a small lens, using an effective region of thelens without waste is required.

Therefore, an object of the present disclosure is to provide a quantumcascade laser device in which an effective region of a lens can beefficiently used.

Solution to Problem

A quantum cascade laser device according to one aspect of the presentdisclosure includes: a quantum cascade laser element; a lens disposed toface an emitting surface of the quantum cascade laser element that emitslaser light; and a lens holder that holds the lens. The lens holderincludes a first hole portion extending in an optical axis directionalong an optical axis of the laser light, a second hole portion that isprovided at a position farther from the quantum cascade laser elementthan the first hole portion, and that includes the first hole portionand is larger than the first hole portion when viewed in the opticalaxis direction, and a counterbore surface having an annular shape thatconnects the first hole portion and the second hole portion and thatextends along a plane intersecting the optical axis direction. The lensincludes an incident surface on which the laser light is incident, and aside surface extending from an edge portion of the incident surfacealong the optical axis direction. At least a part of the side surface isfixed to an inner surface of the second hole portion through a resinadhesive agent in a state where the edge portion of the incident surfaceis in contact with the counterbore surface. A central axis of the firsthole portion is eccentric from a central axis of the second holeportion. The side surface of the lens is positioned with respect to theinner surface of the second hole portion along a direction from thecentral axis of the second hole portion toward the central axis of thefirst hole portion. A central axis of the lens is disposed at a positioncloser to the central axis of the first hole portion than to the centralaxis of the second hole portion.

In the quantum cascade laser device, the lens holder includes the firsthole portion and the second hole portion of which the central axes areeccentric with respect to each other. In addition, the side surface ofthe lens is positioned with respect to the inner surface of the secondhole portion along the direction from the central axis of the secondhole portion toward the central axis of the first hole portion.Accordingly, the positional offset of the lens (movement of the lenswith respect to the lens holder) that may be caused by the surfacetension of the resin adhesive agent disposed around the lens in casethat the lens is disposed at a central portion of the second holeportion can be suitably suppressed. Further, the central axis of thelens is disposed at a position close to the central axis of the firsthole portion in a state where the lens is positioned in such a manner.Accordingly, the area of a region in which an effective region of thelens (region within an effective diameter around the central axis of thelens) and the counterbore surface interfere with (overlap) each othercan be reduced. As a result, the effective region of the lens can beefficiently used.

The central axis of the lens may substantially coincide with the centralaxis of the first hole portion, and an effective diameter of the lensmay substantially coincide with a diameter of the first hole portion.According to this configuration, the entirety of the effective region(region within the effective diameter) of the lens can be exposedthrough the first hole portion. Accordingly, the size of the first holeportion is suppressed to its minimum to secure the area of thecounterbore surface, so that it is possible to make the most use of theeffective region of the lens while appropriately supporting the edgeportion of the incident surface of the lens.

A recess that reaches the counterbore surface along the optical axisdirection may be formed in the inner surface of the second hole portion,and the resin adhesive agent may enter the recess. According to thisconfiguration, the resin adhesive agent can be easily injected into agap between the side surface of the lens and the inner surface of thesecond hole portion through the recess.

The quantum cascade laser device may further include a heat spreader onwhich the lens holder is mounted. The lens holder may have a firstattachment surface on which a plurality of first protrusions protrudingto a heat spreader side are formed, and the plurality of firstprotrusions may be joined to a second attachment surface of the heatspreader through an adhesive layer made of a photocurable resin.According to this configuration, since locations where the adhesivelayer (photocurable resin) is provided can be dispersed onto theplurality of first protrusions, the adhesive layer on each of the firstprotrusions can be easily and appropriately cured compared to when theadhesive layer is provided in a wide range on the entire surface.

A plurality of second protrusions protruding to a lens holder side maybe formed on the second attachment surface at positions corresponding tothe plurality of first protrusions, and the plurality of firstprotrusions may be joined to the plurality of second protrusions throughthe adhesive layer. According to this configuration, the adhesive layeris disposed at a central portion of a space formed between the firstattachment surface and the second attachment surface. Accordingly, theadhesive layer can be suitably irradiated with light reflected by thefirst attachment surface and by the second attachment surface in thespace. As a result, the adhesive layer can be more appropriately cured,and the lens holder can be stably fixed to the heat spreader.

A first wall portion having the first attachment surface of the lensholder may be provided with a through-hole or a cutout for guiding lightto the second attachment surface of the heat spreader. According to thisconfiguration, the second attachment surface of the heat spreader can beirradiated with light from a side opposite to a side on which the heatspreader is disposed with respect to the lens holder, through thethrough-hole or the cutout provided in the first wall portion.Accordingly, light irradiation for curing the adhesive layer between thefirst attachment surface and the second attachment surface can be easilyperformed.

The lens holder may include a second wall portion facing the first wallportion through the second hole portion, and the second wall portion maybe formed not to overlap at least a part of the through-hole or thecutout provided in the first wall portion, when viewed in a direction inwhich the first wall portion and the second wall portion face eachother. According to this configuration, the lens disposed in the secondhole portion can be appropriately protected from the outside by thefirst wall portion and the second wall portion. In addition, since thesecond wall portion is formed not to overlap at least a part of thethrough-hole or the cutout provided in the first wall portion, thesecond attachment surface of the heat spreader can be irradiated withlight by irradiating the lens holder with the light from the outside ofthe lens holder (side opposite to the first wall portion with the secondwall portion sandwiched therebetween).

The quantum cascade laser element and the lens holder may be mounted onthe same heat spreader. According to this configuration, since a base(heat spreader) on which the quantum cascade laser element and the lensholder are placed is shared, when the heat spreader expands or contractsbecause of heat, a relative movement of the lens holder with respect tothe quantum cascade laser element can be suppressed. As a result, theoccurrence of an optical axis offset (offset of the central axis of thelens with respect to the optical axis of the laser light emitted fromthe quantum cascade laser element) caused by a temperature change in thepackage can be suppressed.

The quantum cascade laser device may further include a package thatairtightly accommodates the quantum cascade laser element, the lens, andthe lens holder. The package may include a bottom wall, a side wallstanding on the bottom wall and being formed in an annular shape tosurround a region in which the quantum cascade laser element and thelens holder are accommodated, when viewed in a direction perpendicularto the bottom wall, and a top wall that closes an opening on an oppositeside of the side wall from a bottom wall side. A light-emitting windowthrough which the laser light that has passed through the lens passesmay be provided on the side wall. According to this configuration, asdescribed above, since the effective region of the lens disposed in thepackage can be efficiently used, the size of the lens can be reduced,and the size of the package can be reduced.

Advantageous Effects of Invention

According to the present disclosure, it is possible to provide thequantum cascade laser device in which the effective region of the lenscan be efficiently used.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of a quantum cascade laser device of oneembodiment.

FIG. 2 is a side cross-sectional view of the quantum cascade laserdevice shown in FIG. 1 .

FIG. 3 is a plan view of the quantum cascade laser device shown in FIG.1 .

FIG. 4 is a graph showing a typical example of a relationship betweenthe radiation angle (horizontal axis) and the radiation intensity(vertical axis) of laser light emitted by a quantum cascade laser.

FIG. 5 is a partial enlarged view of the quantum cascade laser deviceshown in FIG. 1 .

FIG. 6 is a front view of a portion of a side wall including asmall-diameter hole and a large-diameter hole.

(A) of FIG. 7 is a view showing an incident surface of a window member,(B) of FIG. 7 is a cross-sectional view of the window member, and (C) ofFIG. 7 is a view showing an emitting surface of the window member.

(A) of FIG. 8 is a top view of a Peltier module, and (B) of FIG. 8 is aside view of the Peltier module.

(A) of FIG. 9 is a top view of a heat spreader, (B) of FIG. 9 is a sideview of the heat spreader, and (C) of FIG. 9 is a bottom view of theheat spreader.

(A) of FIG. 10 is a top view of a heat sink on which each element ismounted, and (B) of FIG. 10 is a side view of the heat sink on whicheach element is mounted.

FIG. 11 is a perspective view of a lens holder.

FIG. 12 is a front view of the lens holder.

(A) of FIG. 13 is a top view of the lens holder, (B) of FIG. 13 is abottom view of the lens holder, and (C) of FIG. 13 is a sidecross-sectional view of the lens holder.

FIG. 14 is a view schematically showing a cross section taken along lineXIV-XIV in FIG. 12 .

FIG. 15 is a view schematically showing a positional relationshipbetween a lens and a lens holder when the lens holder according to acomparative example is used.

FIG. 16 is a view showing a part of an assembly procedure of the quantumcascade laser device shown in FIG. 1 .

(A) of FIG. 17 is a front view of a lens holder of a first modificationexample, and (B) of FIG. 17 is a cross-sectional view of the lens holdertaken along line B-B of (A) of FIG. 17 .

(A) of FIG. 18 is a front view of a lens holder of a second modificationexample, and (B) of FIG. 18 is a cross-sectional view of the lens holdertaken along line B-B of (A) of FIG. 18 .

(A) of FIG. 19 is a front view of a lens holder of a third modificationexample, and (B) of FIG. 19 is a cross-sectional view of the lens holdertaken along line B-B of (A) of FIG. 19 .

FIG. 20 is a side cross-sectional view of a quantum cascade laser deviceof a modification example.

DESCRIPTION OF EMBODIMENTS

Hereinafter, an embodiment of the present disclosure will be describedwith reference to the drawings. In the drawings, the same or equivalentportions are denoted by the same reference signs, and a duplicateddescription will not be repeated. Incidentally, in the drawings, someportions may be exaggerated for an easy-to-understand description ofconfigurations according to the embodiment, and have dimensionsdifferent from actual dimensions. In addition, in the followingdescription, the terms “up”, “down”, and the like are for conveniencebased on states shown in the drawings.

As shown in FIGS. 1 to 3 , a quantum cascade laser device 1(semiconductor laser device) includes a quantum cascade laser element(hereinafter, “QCL element”) 2 and a package 3 that airtightlyaccommodates the QCL element 2.

The QCL element 2 is one type of semiconductor laser element. The QCLelement 2 has an end surface 2 a (emitting surface) intersecting onedirection (in the present embodiment, an X-axis direction), and isconfigured to emit laser light L having a broadband wavelength (forexample, 4 μm to 12 μm) in a mid-infrared region from the end surface 2a. In the present embodiment, an optical axis of the laser light Lemitted from the QCL element 2 is disposed along the X-axis direction.The QCL element 2 has, for example, a structure in which a plurality ofactive layers having different center wavelengths are stacked in astack, and can emit the above-described broadband light. However, theQCL element 2 may have a structure including a single active layer, andin this case as well, can emit the above-described broadband light. Asshown in FIG. 4 , the laser light L emitted from the QCL element 2 has avery large beam radiation angle (divergence angle) as per the principleof a quantum cascade laser compared to a laser diode or the like.

The package 3 is a so-called butterfly package. The package 3 includes abottom wall 31, a side wall 32, and a top wall 33. In FIG. 3 , the topwall 33 of the package 3 is not shown.

The bottom wall 31 is a rectangular plate-shaped member. The bottom wall31 is made of, for example, a metal material such as copper-tungsten.The bottom wall 31 is a base member on which various members such as aPeltier module 4 to be described later are to be mounted. In thisspecification, for convenience, a longitudinal direction of the bottomwall 31 is referred to as the X-axis direction, a lateral direction ofthe bottom wall 31 is referred to as a Y-axis direction, and a directionperpendicular to the bottom wall 31 (namely, a direction orthogonal tothe X-axis direction and to the Y-axis direction) is referred to as aZ-axis direction. As described above, the X-axis direction is also adirection along the optical axis of the laser light L emitted from theQCL element 2 (optical axis direction).

The side wall 32 stands on the bottom wall 31. When viewed in the Z-axisdirection, the side wall 32 is formed in an annular shape to surround aregion (internal space S) in which the QCL element 2 and the like areaccommodated. In the present embodiment, the side wall 32 is arectangular tubular member that surrounds the internal space S. The sidewall 32 is made of a metal material such as Kovar. The side wall 32 is,for example, a Kovar frame to which Ni/Au plating is applied. In thepresent embodiment, the side wall 32 is provided on a central portion ofthe bottom wall 31 in the longitudinal direction (X-axis direction). Awidth of the side wall 32 in the lateral direction (Y-axis direction) isequal to a width of the bottom wall 31 in the lateral direction, and awidth of the side wall 32 in the longitudinal direction (X-axisdirection) is shorter than a width of the bottom wall 31 in thelongitudinal direction. Namely, protrusion portions 31 a protruding andextending outward from the side wall 32 are formed on both respectivesides of the bottom wall 31 in the longitudinal direction. Screw holes31 b for attaching the package 3 (bottom wall 31) to another member areprovided in respective portions of the protrusion portions 31 acorresponding to four corners of the bottom wall 31.

The top wall 33 is a member that closes an opening on an opposite sideof the side wall 32 from a bottom wall 31 side. The top wall 33 has arectangular plate shape. An outer shape (widths in the longitudinaldirection and in the lateral direction) of the top wall 33 viewed in theZ-axis direction substantially coincides with an outer shape of the sidewall 32. The top wall 33 is made of, for example, the same metalmaterial (for example, Kovar or the like) as that of the side wall 32.

A plurality (in the present embodiment, seven on each of both sides inthe lateral direction, for a total of 14) of lead pins 10 for allowing acurrent to flow to members such as the QCL element 2 accommodated in thepackage 3 are inserted into portions 321 of the side wall 32 extendingalong the longitudinal direction (X-axis direction) (namely, portionsintersecting the lateral direction (Y-axis direction)).

A light-emitting window 11 through which the laser light L emitted fromone end surface 2 a of the QCL element 2 passes is provided on one ofportions 322 of the side wall 32 extending along the lateral direction(Y-axis direction) (namely, portions intersecting the longitudinaldirection (X-axis direction)).

As shown in FIGS. 5 and 6 , the light-emitting window 11 includes asmall-diameter hole 12, a large-diameter hole 13, a counterbore surface14, which are formed by the side wall 32 (portion 322), and a windowmember 15. Incidentally, anti-reflection films 151 and 152 and a metalfilm 153 to be described later are provided on the window member 15(refer to FIG. 7 ). Since these members are very thin compared to a mainbody of the window member 15, these members are not shown in thedrawings other than FIG. 7 .

The small-diameter hole 12 opens to the inside (namely, the internalspace S) of the package 3 in the optical axis direction along theoptical axis of the laser light L (namely, the X-axis direction). Thelarge-diameter hole 13 opens to the outside of the package 3. Thelarge-diameter hole 13 is shaped to include the small-diameter hole 12and to be larger than the small-diameter hole 12 when viewed in theX-axis direction. Each of the small-diameter hole 12 and thelarge-diameter hole 13 extends in the X-axis direction. Thesmall-diameter hole 12 and the large-diameter hole 13 connected to eachother by the counterbore surface 14 forms a through-hole penetratingthrough the side wall 32 in the X-axis direction. In the presentembodiment, each of the small-diameter hole 12 and the large-diameterhole 13 is formed in a circular shape, and a diameter d2 of thelarge-diameter hole 13 is larger than a diameter d1 of thesmall-diameter hole 12 (d2>d1). In addition, a central axis of thesmall-diameter hole 12 and a central axis of the large-diameter hole 13may coincide with the optical axis of the laser light L emitted from theQCL element 2. The counterbore surface 14 is an annular surface thatconnects the small-diameter hole 12 and the large-diameter hole 13, andthat extends along a plane intersecting the X-axis direction (Y-Zplane). More specifically, the counterbore surface 14 connects an endportion on a large-diameter hole 13 side of the small-diameter hole 12and an end portion on a small-diameter hole 12 side of thelarge-diameter hole 13. The large-diameter hole 13 and the counterboresurface 14 can be formed by performing counterbore processing from theoutside of the package 3. Incidentally, in the present embodiment, thecounterbore surface 14 is formed in a continuous annular shape, but thecounterbore surface 14 may be formed in a discontinuous annular shape.For example, a cutout may be formed at a part of an inner wall surfaceof the small-diameter hole 12 to divide the counterbore surface 14 atthe portion at which the cutout is formed.

In the present embodiment, the diameter d1 of the small-diameter hole 12is 3.8 mm, the diameter d2 of the large-diameter hole 13 is 5.7 mm, anda width of the counterbore surface 14 in a radial direction ((d2−d1)/2)is 0.95 mm. In addition, a length w1 of the small-diameter hole 12 alongthe X-axis direction is shorter than a length w2 of the large-diameterhole 13 along the X-axis direction. In the present embodiment, athickness t (length along the X-axis direction) of the side wall 32 is 1mm, the length w1 of the small-diameter hole 12 is 0.23 mm, and thelength w2 of the large-diameter hole 13 is 0.77 mm.

The window member 15 is made of a material (for example, germanium orthe like) that transmits the laser light L having a wavelength in themid-infrared region. The window member 15 is formed in a disk shape, andis disposed inside the large-diameter hole 13. The window member 15 hasan incident surface 15 a, an emitting surface 15 b, and a side surface15 c. The incident surface 15 a and the emitting surface 15 b aresurfaces intersecting the X-axis direction, and are formed in a circularshape. The incident surface 15 a is a surface on an internal space Sside, and is a surface on which the laser light L (in the presentembodiment, the laser light L collimated by a lens 8) is incident. Theemitting surface 15 b is a surface opposite to the incident surface 15 a(namely, an outer surface of the package 3), and a surface that emitsthe laser light L that has transmitted through the window member 15, tothe outside of the package 3. The side surface 15 c is a surface thatconnects the incident surface 15 a and the emitting surface 15 b, andthat extends along the X-axis direction. In the present embodiment, adiameter of the window member 15 (the incident surface 15 a or theemitting surface 15 b) is 5.4 mm, and a thickness (length along theX-axis direction) of the window member 15 is 0.7 mm.

As shown in (A) and (B) of FIG. 7 , the incident surface 15 a includes afirst region A1 and a second region A2. The first region A1 is a regionwhich includes a central portion of the incident surface 15 a and inwhich the anti-reflection film 151 (first anti-reflection film) isprovided. The anti-reflection film 151 is a film member having afunction of suppressing the reflection of the laser light L having awavelength in the mid-infrared region on the incident surface 15 a. Theanti-reflection film 151 is made of, for example, a high refractiveindex material such as germanium (Ge) or silicon (Si), an intermediaterefractive index material such as zinc sulfide (ZnS) or zinc selenide(ZnSe), or a low refractive index material such as yttrium fluoride(YF3), or is a dielectric multilayer film in which a plurality ofsubstances having different refractive indexes that transmitmid-infrared light are alternately stacked. The anti-reflection film 151is formed in a circular shape. A thickness (length along the X-axisdirection) of the anti-reflection film 151 is determined according tothe design of a transmission wavelength of the anti-reflection film 151(wavelength of the laser light L that is transmitted). The thickness ofthe anti-reflection film 151 is, for example, 1.0 μm to 3.0 μm. Forexample, when a design value of the transmission wavelength is 5.2 μm,the thickness of the anti-reflection film 151 is set to, for example,1.4 μm. In addition, in the present embodiment, a diameter of theanti-reflection film 151 (namely, a diameter of the first region A1) is4.2 mm.

The second region A2 is a region formed in an annular shape to beseparated from the first region A1 and to surround the first region A1.The second region A2 is metallized by the metal film 153. The metal film153 is made of a material suitable for solder joining (namely, amaterial having good compatibility with a solder member 16 to bedescribed later). The metal film 153 is made of, for example, Cr/Ni/Au(0.2 μm/0.5 μm/0.5 μm). In the present embodiment, an inner diameter ofthe metal film 153 (namely, an inner diameter of the second region A2)formed on the incident surface 15 a is 4.5 mm. Namely, in the presentembodiment, an annular region having a width of 0.15 mm in which theincident surface 15 a (germanium base material) is exposed is formedbetween an outer edge of the first region A1 and an inner edge of thesecond region A2.

As shown in (B) of FIG. 7 , the side surface 15 c includes a thirdregion A3 metallized to be continuous with the second region A2. Namely,the metal film 153 is continuously provided from the second region A2 tothe side surface 15 c.

As shown in (B) and (C) of FIG. 7 , the emitting surface 15 b includes afourth region A4 in which the anti-reflection film 152 (secondanti-reflection film) is provided. The anti-reflection film 152 is afilm member having a function of suppressing the reflection of the laserlight L having a wavelength in the mid-infrared region on the emittingsurface 15 b. The anti-reflection film 152 is formed in a circular shapefrom the same material as that of the anti-reflection film 151. In thepresent embodiment, a diameter of the anti-reflection film 152 (namely,a diameter of the fourth region A4) is 4.6 mm. Namely, the fourth regionA4 is a region that includes the first region A1 and that is larger thanthe first region A1 when viewed in the X-axis direction.

The window member 15 is directly joined to the side wall 32 (portion322). Specifically, the second region A2 of the incident surface 15 a(namely, a region metallized by the metal film 153) is joined to thecounterbore surface 14 through the solder member 16 formed in an annularshape. The solder member is a joining material having a melting point of450° C. or lower. The solder member 16 is made of, for example, aSnAgCu-based solder material having a melting point of 220° C. Thesolder member 16 is a sheet-shaped member that is originally formed inan annular shape (refer to FIG. 16 ).

In the present embodiment, a thickness of the solder member 16 beforesoldering (namely, in the state of an annular sheet) is 0.1 mm, an outerdiameter thereof is 5.5 mm, and an inner diameter thereof is 4.2 mm.Namely, in the present embodiment, the inner diameter (4.2 mm) of thesolder member 16 is equal to the diameter (4.2 mm) of the first regionA1, and the first region A1 and the solder member 16 do not overlap eachother. In addition, the first region A1 in which the anti-reflectionfilm 151 is formed and the second region A2 in which the metal film 153is formed are separated from each other. In such a manner, since thefirst region A1 and the second region A2 are completely separated fromeach other, and the region in which the base material (in the presentembodiment, germanium base material) of the window member 15 is exposedexists between the first region A1 and the second region A2, duringsoldering, the solder member 16 is unlikely to flow onto the firstregion A1 (onto the anti-reflection film 151). On the other hand, thesolder member 16 is likely to wet-spread on the metal film 153 havinghigh compatibility with the solder member 16. Accordingly, stressgenerated when the solder member 16 is melted or solidified duringsoldering is unlikely to be transmitted to the anti-reflection film 151on the first region A1.

In addition, as described above, since the solder member 16 wet-spreadson the metal film 153, some of the solder member 16 also wraps aroundonto the third region A3 (refer to FIG. 5 ). Namely, some of the soldermember 16 enters a gap between the side surface 15 c and an innersurface of the large-diameter hole 13. Namely, at least a part of theside surface 15 c of the window member 15 is joined to at least a partof the inner surface of the large-diameter hole 13 through the soldermember 16. Accordingly, the airtightness of the package 3 at anattachment portion of the window member 15 is effectively enhanced.

In the present embodiment, the emitting surface 15 b of the windowmember 15 is substantially flush with an outer surface 32 a of the sidewall 32 (outer surface of the package 3) on which the light-emittingwindow 11 is provided. Namely, the length w2 of the large-diameter hole13 (namely, a depth of counterbore processing) is adjusted such that theemitting surface 15 b is substantially flush with the outer surface 32 aof the side wall 32.

Next, each member accommodated in the package 3 will be described. Theinternal space S formed by the package 3 mainly accommodates the Peltiermodule 4, a heat spreader 5, a heat sink 6, a submount 7, the lens 8, alens holder 9, and a temperature sensor T (refer to FIG. 10 ) inaddition to the QCL element 2.

The Peltier module 4 is a temperature control element that adjusts thetemperature of the QCL element 2. Specifically, the Peltier module 4 hasa cooling and heating function of keeping the temperature of the QCLelement 2 at a temperature corresponding to the oscillation wavelengthof the QCL element 2. Temperature control by the Peltier module 4 isperformed based on the temperature of the QCL element 2 measured by thetemperature sensor T (refer to FIG. 10 ) to be mounted on the heat sink6.

As shown in FIG. 8 , the Peltier module 4 includes a plurality ofPeltier elements 41 that are thermoelectric semiconductor elements, anda pair of ceramic substrates 42 and 43 that sandwich the plurality ofPeltier elements 41 therebetween from above and below. The ceramicsubstrate 42 is provided on a top wall 33 side with respect to thePeltier elements 41, and the ceramic substrate 43 is provided on thebottom wall 31 side with respect to the Peltier elements 41. Each of theceramic substrates 42 and 43 is made of, for example, alumina. An outersurface of each of the ceramic substrates 42 and 43 (surface opposite toa Peltier element 41 side) is a metallized surface on which a metal film44 made of Cu/Ni/Au or the like is formed by plating. An In foil 45 thatis a solder member is provided on the outer surface of each of theceramic substrates 42 and 43 with the metal film 44 interposedtherebetween. The ceramic substrate 42 is solder joined to the heatspreader 5 through the In foil 45. On the other hand, the ceramicsubstrate 43 is solder joined to an upper surface 31 c (surface facingthe top wall 33) of the bottom wall 31 of the package 3 through the Infoil 45. Two lead wires 20 for allowing a direct current to flow to thePeltier module 4 are electrically connected to one ceramic substrate (inthe present embodiment, the ceramic substrate 43). The two lead wires 20are connected to different respective lead pins 10.

The heat spreader 5 is a member to be mounted on the Peltier module 4,and dissipates heat generated by the QCL element 2, to a Peltier module4 side. The heat spreader 5 is made of, for example, a material havinggood thermal conductivity such as copper. As shown in FIG. 9 , the heatspreader 5 has a bottom surface 51 to be solder joined to the Peltiermodule 4 through the In foil 45 (refer to FIG. 8 ) provided on theceramic substrate 42; a first upper surface 52 on which the heat sink 6and the submount 7 are to be mounted; and a second upper surface 53(second attachment surface) on which the lens holder 9 is to be mounted.

Here, a thermal expansion coefficient of copper (approximately17×10⁻⁶/K) is larger than a thermal expansion coefficient of alumina(approximately 7×10⁻⁶/K). For this reason, when the ceramic substrate 42of the Peltier module 4 is made of alumina and the heat spreader 5 ismade of copper, if the entirety of the bottom surface 51 of the heatspreader 5 is joined to the ceramic substrate 42 through the In foil 45,cracks might occur in the Peltier elements 41 because of a largedifference in temperature or the like between upper surfaces and lowersurfaces of the Peltier elements 41 during the long-term use,temperature control, or the like of the quantum cascade laser device 1,which is a problem.

Therefore, in the present embodiment, groove portions 51 a that divide asurface to be joined to the Peltier module 4 into a plurality ofsegments are formed in the bottom surface 51 of the heat spreader 5. Inthe present embodiment, as one example, two groove portions 51 a extendalong the lateral direction (Y-axis direction) at positions where thebottom surface 51 is divided into three segments in the longitudinaldirection (X-axis direction). The surface to be joined to the Peltiermodule 4 is substantially evenly into three segments by the two grooveportions 51 a. In such a manner, since the surface to be joined to thePeltier module 4 is divided into a plurality (here, three) of segments,the stress caused by a difference in thermal expansion coefficientbetween the material (alumina) of the ceramic substrate 42 and thematerial (copper) of the heat spreader 5 is reduced, and the occurrenceof cracks in the Peltier elements 41 described above is suppressed.

In addition, four corners (vertexes) of the Peltier module 4 are weakparticularly in mechanical strength. Therefore, in the presentembodiment, cutout grooves 51 b are formed at four corners of the bottomsurface 51 of the heat spreader 5. Accordingly, the ceramic substrate 42and the bottom surface 51 of the heat spreader 5 can be prevented frombeing joined to each other at portions corresponding to the four cornersof the Peltier module 4, and the stress on the four corners of thePeltier module 4 caused by the difference in thermal expansioncoefficient can be effectively reduced.

Incidentally, the groove portions 51 a and the cutout grooves 51 bdescribed above also function as escape routes of air layers (voids)that are mixed when the ceramic substrate 42 and the bottom surface 51are solder joined to each other through the In foil 45. Accordingly, thequality of joining and the thermal conductivity between the Peltiermodule 4 (ceramic substrate 42) and the heat spreader 5 can be improved.

In addition, since a soft solder material such as In or InSn (in thepresent embodiment, In) is used as a solder member that joins thePeltier module 4 (ceramic substrate 42) and the heat spreader 5, thestress of expansion or contraction by heat can be suitably absorbed, andthe reliability of the quantum cascade laser device 1 can be improved.

The first upper surface 52 is located at a position higher than that ofthe second upper surface 53 (top wall 33 side). In the presentembodiment, as one example, the first upper surface 52 is provided withtwo screw holes 52 a for screwing the heat sink 6 and with a protrusionportion 52 b protruding upward (top wall 33 side). The protrusionportion 52 b extends along the lateral direction (Y-axis direction) atan end portion of the first upper surface 52 in the longitudinaldirection (X-axis direction) (end portion opposite to a second uppersurface 53 side). The protrusion portion 52 b is a portion that comesinto contact with an end portion of the heat sink 6 to position the heatsink 6.

The second upper surface 53 is provided with a plurality (in the presentembodiment, four) of protrusions 53 a (second protrusions) formed in anisland shape. The four protrusions 53 a are portions to be joined to thelens holder 9 to be described later.

The heat sink 6 is a member to be mounted on the first upper surface 52of the heat spreader 5. Similarly to the heat spreader 5, the heat sink6 is made of, for example, a material having good thermal conductivitysuch as copper. The heat sink 6 is formed in a substantially rectangularparallelepiped shape. For example, a width of the heat sink 6 along theX-axis direction is 5 mm, and a width of the heat sink 6 along theY-axis direction is 6 mm. As shown in FIG. 10 , the submount 7 on whichthe QCL element 2 is mounted, the temperature sensor T that measures atemperature of the QCL element 2, and ceramic patterns SP for wiringwires are mounted on an upper surface 6 a (surface on the top wall 33side) of the heat sink 6. A lower surface 6 b of the heat sink 6 is incontact with the first upper surface 52 of the heat spreader 5. In orderto enable the QCL element 2 to be easily replaced when a defect occursin the QCL element 2, the heat sink 6 is fixed to the heat spreader 5with screws. Screw holes 6 c penetrating through the heat sink 6 in theZ-axis direction, and counterbore grooves 6 d formed around the screwholes 6 c are formed in the heat sink 6 for such screwing. The screwholes 6 c are provided at positions corresponding to the screw holes 52a (refer to FIG. 9 ) of the heat spreader 5 described above. Forexample, the heat sink 6 is fixed to the heat spreader 5 by insertingscrew members (not shown) into the screw holes 6 c and into the screwholes 52 a, screw tips of the screw members being coated with a screwlocking agent (adhesive agent for preventing the loosening of screws).Each of the counterbore grooves 6 d is a groove portion provided toaccommodate a head of the screw member. Incidentally, as the screwlocking agent, a thermosetting resin adhesive agent that does notgenerate outgas (for example, epoxy resin or the like) is suitably used.

The temperature sensor T and the ceramic patterns SP are electricallyconnected to predetermined lead pins 10 through wires (not shown). Inaddition, the QCL element 2 is electrically connected to a predeterminedlead pin 10 through the ceramic patterns SP and through wires (notshown). Accordingly, electric power is supplied from an external powersupply device to the QCL element 2 and to the temperature sensor Tthrough the lead pins 10.

The submount 7 is a rectangular plate-shaped member on which the QCLelement 2 is to be placed. The QCL element 2 is placed on the submount 7such that the optical axis of the laser light L emitted from the endsurface 2 a coincides with a center of the light-emitting window 11(namely, the central axes of the small-diameter hole 12 and thelarge-diameter hole 13). The submount 7 is made of a material having athermal expansion coefficient close to that of the QCL element 2 (forexample, aluminum nitride or the like). The QCL element 2 and thesubmount 7 are joined to each other through, for example, an AnSn-basedsolder material. In addition, the submount 7 and the heat sink 6 arejoined to each other through, for example, a SnAgCuNiGe-based soldermaterial.

Subsequently, the lens 8 and the lens holder 9 will be described withreference to FIGS. 11 to 15 . As described above, the laser light L hasa relatively large beam radiation angle as per the principle of aquantum cascade laser (refer to FIG. 4 ). For this reason, in order toeffectively use the laser light L, it is necessary to perform beamshaping (concentrating, collimating, or the like) of the laser light Lusing an optical element such as a lens. On the other hand, since thelaser light L having an oscillation wavelength in the mid-infraredregion is invisible, an expensive beam monitor, detector, or the likehaving sensitivity in the mid-infrared region is required to perform analignment (position alignment) of the lens for the beam shaping.Therefore, in the present embodiment, the lens 8 for performing the beamshaping is built in inside the package 3 in advance. This configurationhas an advantage that it is not necessary to perform an alignment of alens (lens to be externally attached) on a user side.

The lens 8 is a member that concentrates or collimates the laser light Lemitted from the QCL element 2. The lens holder 9 is a member that holdsthe lens 8. The lens 8 is disposed to face the end surface 2 a that isthe emitting surface of the QCL element 2 that emits the laser light L.

The lens 8 is, for example, an aspherical lens made of ZnSe. As shown inFIGS. 11 and 14 , the lens 8 has an incident surface 8 a, a side surface8 b, and an emitting surface 8 c. The incident surface 8 a is a surfaceon which the laser light L is incident. In the present embodiment, theincident surface 8 a is a flat surface. The side surface 8 b is asurface extending from an edge portion of the incident surface 8 a alongthe optical axis direction (namely, the X-axis direction) of the laserlight L. The emitting surface 8 c is a surface that emits the laserlight L that has passed through the lens 8. In the present embodiment,the emitting surface 8 c is formed in a curved aspherical surface shape.In the present embodiment, a diameter of the lens 8 (diameter of theincident surface 8 a) is 5 mm, and an effective diameter of the lens 8is 4.5 mm. The effective diameter of the lens 8 is a diameter of anincident beam capable of satisfying optical characteristics of the lenson a plane (incident surface 8 a) orthogonal to the optical axisdirection (X-axis direction) of the laser light L (when the lens 8 is acollimating lens, a diameter of incident light that can be transmittedand collimated, as a specification of the lens). In addition, a regionwithin the effective diameter of the lens 8 is referred to as aneffective region.

As shown in FIG. 11 , the lens holder 9 is a member having asubstantially rectangular parallelepiped outer shape. The lens holder 9is made of, for example, aluminum to which black alumite surfacetreatment is applied. A through-hole penetrating through the lens holder9 along the X-axis direction is provided in a central portion of thelens holder 9 when viewed in the X-axis direction. The lens holder 9 hasa small-diameter hole 9 a (first hole portion) and a large-diameter hole9 b (second hole portion) that form the through-hole. Each of thesmall-diameter hole 9 a and the large-diameter hole 9 b extends in theX-axis direction. The large-diameter hole 9 b is provided at a positionfarther from the QCL element 2 than the small-diameter hole 9 a. Namely,the small-diameter hole 9 a is provided on a QCL element 2 side withrespect to the large-diameter hole 9 b. The large-diameter hole 9 b isshaped to include the small-diameter hole 9 a and to be larger than thesmall-diameter hole 9 a when viewed in the X-axis direction. Thelarge-diameter hole 9 b is formed in a larger size than the outer shapeof the lens 8 such that the lens 8 can be accommodated inside thelarge-diameter hole 9 b. In the present embodiment, each of thesmall-diameter hole 9 a and the large-diameter hole 9 b is formed in acircular shape. The small-diameter hole 9 a and the large-diameter hole9 b are connected to each other by a counterbore surface 9 c having anannular shape and extending along a plane intersecting the X-axisdirection (Y-Z plane). More specifically, the counterbore surface 9 cconnects an end portion on a large-diameter hole 9 b side of thesmall-diameter hole 9 a and an end portion on a small-diameter hole 9 aside of the large-diameter hole 9 b. Incidentally, in the presentembodiment, the counterbore surface 9 c is formed in a continuousannular shape, but the counterbore surface 9 c may be formed in adiscontinuous annular shape. For example, a cutout may be formed at apart of an inner wall surface of the small-diameter hole 9 a to dividethe counterbore surface 9 c at the portion at which the cutout isformed.

As shown in FIGS. 11 and 12 , a groove portion 9 d (recess) that extendsfrom an end portion on an opposite side of the lens holder 9 from theQCL element 2 side to reach the counterbore surface 9 c is formed in aninner surface of the large-diameter hole 9 b along the X-axis direction.In the present embodiment, a pair of the groove portions 9 d facing eachother along one diagonal line of the lens holder 9 having a rectangularshape when viewed in the X-axis direction are formed.

As shown in FIGS. 12 and 14 , a central axis AX1 of the small-diameterhole 9 a does not coincide with a central axis AX2 of the large-diameterhole 9 b. Namely, the central axis AX1 of the small-diameter hole 9 a iseccentric from the central axis AX2 of the large-diameter hole 9 b.Incidentally, in FIG. 14 , the pair of groove portions 9 d are ignoredfor easy understanding of the description. Namely, FIG. 14 is a view inwhich the large-diameter hole 9 b is not provided with the pair ofgroove portions 9 d, and schematically shows a cross-sectional structuretaken along line XIV-XIV of FIG. 12 .

In the present embodiment, the central axis AX1 of the small-diameterhole 9 a is offset with respect to the central axis AX2 of thelarge-diameter hole 9 b in a direction D. The direction D is a directionfrom one groove portion 9 d toward the other groove portion 9 d whenviewed in the X-axis direction. In addition, a diameter d3 of thesmall-diameter hole 9 a is the same as the effective diameter of thelens 8 and is 4.5 mm, and a diameter d4 of the large-diameter hole 9 bis 5.15 mm. In addition, as described above, since the central axis AX1is eccentric with respect the central axis AX2, as shown in FIGS. 12 and14 , a width of the counterbore surface 9 c on a central axis AX1 side(here, a portion excluding the groove portion 9 d) on a straight linepassing through the central axis AX1 and through the central axis AX2 isa minimum width wmin of the counterbore surface 9 c. In addition, awidth of the counterbore surface 9 c on a central axis AX2 side (here, aportion excluding the groove portion 9 d) on the straight line passingthrough the central axis AX1 and through the central axis AX2 is amaximum width wmax of the counterbore surface 9 c. In the presentembodiment, the minimum width wmin is 0.25 mm, the maximum width wmax is0.4 mm, and a distance d between the central axis AX1 and the centralaxis AX2 is 0.075 mm.

An edge portion of the incident surface 8 a of the lens 8 is in contactwith the counterbore surface 9 c. In addition, in the lens 8, the sidesurface 8 b of the lens 8 is positioned with respect to the innersurface of the large-diameter hole 9 b along the direction D from thecentral axis AX2 of the large-diameter hole 9 b toward the central axisAX1 of the small-diameter hole 9 a. Specifically, the side surface 8 bof the lens 8 is abutted against the inner surface of the large-diameterhole 9 b along the direction D. Accordingly, a central axis AX3 of thelens 8 is disposed at a position closer to the central axis AX1 of thesmall-diameter hole 9 a than to the central axis AX2 of thelarge-diameter hole 9 b. In the present embodiment, the diameter (5 mm)and the effective diameter (4.5 mm) of the lens 8, the diameter d3 (4.5mm) of the small-diameter hole 9 a, the diameter d4 (5.15 mm) of thelarge-diameter hole 9 b, and the distance d (0.075 mm) between thecentral axis AX1 and the central axis AX2 are set as described above.Accordingly, the central axis AX3 of the lens 8 substantially coincideswith the central axis AX1 of the small-diameter hole 9 a. Namely, whenviewed in the X-axis direction, the entirety of the effective region ofthe lens 8 overlaps the small-diameter hole 9 a. In other words, theentirety of the effective region of the lens 8 is exposed to the QCLelement 2 side through the small-diameter hole 9 a. Accordingly, it ispossible to make the most use of the effective region of the lens 8.

Next, a method for fixing the lens 8 to the lens holder 9 will bedescribed. As shown in FIG. 14 , at least a part of the side surface 8 bof the lens 8 is fixed to the inner surface of the large-diameter hole 9b through a resin adhesive agent B1 in a state where the lens 8 ispositioned with respect to the lens holder 9 as described above. Theresin adhesive agent B1 is made of, for example, a thermosetting resinsuch as epoxy resin. For example, the resin adhesive agent B1 is pouredinto the groove portions 9 d, so that the resin adhesive agent B1 thathas entered the groove portions 9 d also pours into a gap between theside surface 8 b of the lens 8 and the inner surface of thelarge-diameter hole 9 b on peripheries of the groove portions 9 dbecause of the capillary phenomenon. In addition, the resin adhesiveagent B1 also flows into a gap between the incident surface 8 a of thelens 8 and the counterbore surface 9 c because of the capillaryphenomenon. The resin adhesive agent B1 is cured and the lens 8 is fixedto the lens holder 9 by performing the bake processing of the lensholder 9 in this state. A process of pouring the resin adhesive agent B1into the groove portion 9 d is performed, for example, by inserting aneedle member for coating the resin adhesive agent B1 into the grooveportion 9 d, and by injecting the resin adhesive agent B1 from a tip ofthe needle member toward the counterbore surface 9 c in the grooveportion 9 d. In this case, the groove portions 9 d may be formed in sucha size that the needle member can be inserted thereinto.

Effects obtained by a structure in which the central axis AX1 of thesmall-diameter hole 9 a is eccentric with respect to the central axisAX2 of the large-diameter hole 9 b in the direction D and the lens 8 ispositioned along the direction D (hereinafter, referred to as a“eccentric structure”) will be described in detail with reference toFIG. 15 . FIG. 15 is a view schematically showing a positionalrelationship between the lens 8 and a lens holder 900 when the lensholder 900 according to a comparative example is used. In the lensholder 900, the central axis AX1 of the small-diameter hole 9 a is noteccentric with respect to the central axis AX2 of the large-diameterhole 9 b. Namely, the central axis AX1 and the central axis AX2 coincidewith each other. In this case, in order to make the most use of theeffective diameter of the lens 8, as shown in a left part of FIG. 15 ,it is necessary to cause the central axis AX3 of the lens 8 to coincidewith a central axis (namely, the central axes AX1 and AX2) of the lensholder 900. No problem occurs as long as such a relationship between thelens 8 and the lens holder 900 is maintained. However, in reality, whenthe lens 8 is installed at a center of the lens holder 900 in such amanner, and the side surface 8 b of the lens 8 and the inner surface ofthe large-diameter hole 9 b are joined to each other through the resinadhesive agent B1, as shown in a right part of FIG. 15 , when bakeprocessing is performed, the central axis AX3 of the lens 8 might beoffset from the central axis (central axes AX1 and AX2) of the lensholder 9 because of the surface tension of the resin adhesive agent B1,which is a problem. Specifically, since the amount of the resin adhesiveagent B1 with which the gap between the side surface 8 b of the lens 8and the large-diameter hole 9 b is filled is not always uniform, aphenomenon can occur in which the lens 8 moves in a direction in whichthe surface tension of the resin adhesive agent B1 acts strongly. Whensuch movement (positional offset) of the lens 8 occurs, a part of theeffective region of the lens 8 overlaps the counterbore surface 9 c, andit is not possible to make the most use of the effective region. Namely,as shown in the right part of FIG. 15 , when the central axis AX3 of thelens 8 and the optical axis of the laser light L emitted from the QCLelement 2 are disposed to coincide with each other, light fluxes of thelaser light L cannot be captured in a portion of the effective region ofthe lens 8 overlapping the counterbore surface 9 c.

On the other hand, according to the eccentric structure shown in FIGS.12 and 14 , the side surface 8 b of the lens 8 can be brought into closecontact with the inner surface of the large-diameter hole 9 b along thedirection D in advance, the inner surface serving as an installation endof the lens 8. Then, the closer the distance between the side surface 8b of the lens 8 and the inner surface of the large-diameter hole 9 b atportions (namely, portions in close contact and a periphery thereof) is,the stronger the surface tension of the resin adhesive agent B1 acts.For this reason, even when bake processing is performed, the lens 8 isnot pulled back opposite to the direction D with respect to the lensholder 9. Namely, before and after the bake processing, a state wherethe side surface 8 b of the lens 8 is abutted against the inner surfaceof the large-diameter hole 9 b along the direction D (refer to FIGS. 12and 14 ) is maintained. Therefore, according to the eccentric structure,it is possible to make the most use of the effective region of the lens8 by adjusting dimensions such that the effective region of the lens 8and the small-diameter hole 9 a coincide with each other in a statewhere the lens 8 is positioned as described above.

Incidentally, a portion of the side surface 8 b of the lens 8 and theinner surface of the large-diameter hole 9 b do not necessarily need tobe in direct contact with each other, the portion being abutted againstthe inner surface of the large-diameter hole 9 b. Namely, as shown inFIG. 14 , the resin adhesive agent B1 that has slightly entered a gapbetween the portion of the side surface 8 b of the lens 8 and the innersurface of the large-diameter hole 9 b because of the capillaryphenomenon may be interposed therebetween, the portion being abuttedagainst the inner surface of the large-diameter hole 9 b.

As shown in FIGS. 11, 12 , and (B) of 13, a wall portion 90 (namely, atubular portion extending along the X-axis direction) forming thelarge-diameter hole 9 b of the lens holder 9 includes a bottom wallportion 92 (first wall portion) facing the second upper surface 53 ofthe heat spreader 5. The bottom wall portion 92 has a lower surface 92 a(first attachment surface) facing the second upper surface 53. Aplurality (in the present embodiment, four) of protrusions 92 b (firstprotrusions) protruding to a heat spreader 5 side are formed on thelower surface 92 a. The four protrusions 92 b are provided at positionscorresponding to the four protrusions 53 a (refer to (A) of FIG. 9 )provided on the second upper surface 53 of the heat spreader 5. Theprotrusions 92 b are joined to the respective protrusions 53 a throughan adhesive layer B2 (refer to FIG. 2 ) made of a UV curable resin(photocurable resin).

In the present embodiment, the four protrusions 92 b are disposed atfour corners of the bottom wall portion 92 in a well-balanced manner.Namely, the four protrusions 92 b are disposed such that a center of thefour protrusions 92 b substantially coincides with a center of thebottom wall portion 92 when viewed in the Z-axis direction. Accordingly,the lens holder 9 can be stably fixed onto the second upper surface 53of the heat spreader 5, and a structure that is resistant to impact,vibration, and the like can be realized.

As shown in FIGS. 11 and (A) of 13, the wall portion 90 includes a topwall portion 91 (second wall portion) facing the top wall 33 of thepackage 3. The top wall portion 91 faces the bottom wall portion 92through the large-diameter hole 9 b. A cutout 91 a is formed at an endportion on an opposite side of the top wall portion 91 from thesmall-diameter hole 9 a side. In addition, a cutout 92 c is formed at anend portion on an opposite side of the bottom wall portion 92 from thesmall-diameter hole 9 a side. When viewed in the Z-axis direction, thecutout 91 a and the cutout 92 c include portions overlapping each other.Namely, the top wall portion 91 is formed not to overlap at least a partof the cutout 92 c of the bottom wall portion 92 in a direction in whichthe bottom wall portion 92 and the top wall portion 91 face each other(Z-axis direction). A part of the second upper surface 53 of the heatspreader 5 can be visually recognized from above the top wall portion 91through a portion at which the cutout 91 a and the cutout 92 c overlapeach other. Namely, the second upper surface 53 of the heat spreader 5can be irradiated with light from above the top wall portion 91 throughthe portion. According to such a configuration, UV light can be suitablyguided to a space between the lower surface 92 a of the lens holder 9and the second upper surface 53 of the heat spreader 5 by placing thelens holder 9 on the second upper surface 53 of the heat spreader 5 suchthat the positions of the four protrusions 53 a and the positions of thefour protrusions 92 b are aligned with each other, and then byirradiating the second upper surface 53 with the UV light from above thelens holder 9. Accordingly, the adhesive layer B2 provided between eachof the protrusions 92 b and the corresponding protrusion 53 a can beappropriately cured.

In addition, since locations to be coated with the adhesive layer B2 aredefined by each of the protrusions 92 b and each of the protrusions 53 aformed in an island shape, the locations to be coated with the adhesivelayer B2 and the coating amount of the adhesive layer B2 can beequalized among a plurality of products (quantum cascade laser devices1). In addition, there is a limit to the depth by which UV lightpenetrates into a UV curable resin. For this reason, if the entirety ofthe lower surface 92 a is coated with the UV curable resin withoutproviding the protrusions 92 b and the protrusions 53 a, a problem thatthe UV light does not reach the inside of the UV curable resin (centerside) and the UV curable resin cannot be completely cured can occur.Such a problem can be avoided by defining the locations to be coatedwith the adhesive layer B2 in an island shape as described above. Inaddition, since the protrusions 92 b and the protrusions 53 a areprovided in an island shape, a sufficient space for the passing of theUV light can be formed between the lower surface 92 a and the secondupper surface 53 at positions where the protrusions 92 b and theprotrusions 53 a do not overlap each other. Accordingly, the UV lightthat has entered the space can be reflected by valleys (portions atwhich the protrusions 92 b and the protrusions 53 a are not formed) ofeach of the lower surface 92 a and the second upper surface 53, and theadhesive layer B2 on each of the protrusions 53 a can be irradiated withthe UV light.

Next, a method for manufacturing the quantum cascade laser device 1(assembly method) will be described. As shown in FIG. 16 , first, thepackage 3 before the top wall 33 is joined to the side wall 32 isprepared. Subsequently, the window member 15 (window member 15 on whichthe anti-reflection films 151 and 152 and the metal film 153 areprovided in advance (refer to FIG. 7 )) is joined to the side wall 32.Specifically, the solder member 16 that is an annular sheet membermolded in a washer shape is sandwiched between the counterbore surface14 and the window member 15. Then, a load is applied to the windowmember 15 from the outside of the package 3 to push the window member 15against the counterbore surface 14. In this state, the window member 15and the counterbore surface 14 are joined to each other through thesolder member 16 by using, for example, a vacuum soldering device(vacuum soldering furnace). At this time, a jig for aligning a center ofthe window member 15 with the central axes of the counterbore openings(the small-diameter hole 12 and the large-diameter hole 13) may be used.

Subsequently, the heat spreader 5 is placed on the Peltier module 4 tothe top and the bottom of which the In foils 45 that are solder membersare affixed, and these members are disposed on the bottom wall 31 at apredetermined position using a jig. Then, a load is applied from abovethe heat spreader 5 to push these members against the bottom wall 31. Inthis state, the bottom wall 31, the Peltier module 4, and the heatspreader 5 are joined to each other through the In foils 45 disposedbetween these members, by using, for example, a vacuum soldering device.Subsequently, as shown in FIG. 2 , the lead wires 20 of the Peltiermodule 4 are solder joined to the lead pins 10.

Subsequently, the heat sink 6 on which elements such as the QCL element2, the submount 7, the temperature sensor T, and the ceramic patterns SPare mounted in advance is fixed to the first upper surface 52 of theheat spreader 5. Specifically, the heat sink 6 is screwed to the heatspreader 5 by inserting screw members (not shown) into the screw holes 6c of the heat sink 6 (refer to FIG. 10 ) and into the screw holes 52 aof the heat spreader 5. In addition, the temperature sensor T and theceramic patterns SP are electrically connected to the predetermined leadpins 10 by wires (not shown).

Subsequently, the lens holder 9 on which the lens 8 is mounted asdescribed above is fixed to the second upper surface 53 of the heatspreader 5. Specifically, each of the protrusions 53 a formed on thesecond upper surface 53 of the heat spreader 5 is coated with a UVcurable resin (adhesive layer B2) in advance. Then, the lens holder 9 isvacuum-chucked using, for example, Convum (vacuum generator) or thelike, and is moved into the package 3. Then, the QCL element 2 is drivento emit the laser light L, and an active alignment is performed to alignthe optical axis of the laser light L and the central axis of the lens 8with each other while observing the laser light L using a beam monitor.

Subsequently, the lens holder 9 is fixed to the heat spreader 5 in astate where the positions of the optical axis of the laser light L andthe central axis of the lens 8 are aligned with each other.Specifically, in a state where the optical axis of the laser light L andthe central axis of the lens 8 are aligned with each other, the secondupper surface 53 of the heat spreader 5 is irradiated with UV light fromabove the lens holder 9 through the cutout 91 a and the cutout 92 c ofthe lens holder 9. Accordingly, each of the protrusions 92 b of the lensholder 9 and the corresponding protrusion 53 a of the heat spreader 5are joined to each other through the adhesive layer B2.

Here, the position of each of the protrusions 92 b is designed so as tooverlap the corresponding protrusion 53 a of the heat spreader 5 in astate where the optical axis of the laser light L and the central axisof the lens 8 are aligned with each other. In addition, the heightdimension (length along the Z-axis direction) of each of the protrusions53 a and each of the protrusions 92 b is designed such that a gap ofapproximately several hundreds of μm smaller than the thickness of theUV curable resin (adhesive layer B2) coated on each of the protrusions53 a in advance is formed between each of the protrusions 53 a of theheat spreader 5 and the corresponding protrusion 92 b of the lens holder9 in a state where the optical axis of the laser light L and the centralaxis of the lens 8 are aligned with each other. Accordingly, when thelens holder 9 is moved with respect to the heat spreader 5 to align theoptical axis of the laser light L and the central axis of the lens 8with each other, an adjustment is made such that each of the protrusions92 b of the lens holder 9 and the adhesive layer B2 on the correspondingprotrusion 53 a of the heat spreader 5 come into contact with eachother. In other words, the height dimension of each of the protrusions53 a and each of the protrusions 92 b and the thickness of the adhesivelayer B2 are designed such that the optical axis of the laser light Land the central axis of the lens 8 are aligned with each other in astate where the lens holder 9 is pushed against the UV curable resin(adhesive layer B2) coated on the heat spreader 5 in advance.

Subsequently, an upper end portion of the side wall 32 of the package 3(end portion opposite to the bottom wall 31 side) is joined to the topwall 33. As described above, the quantum cascade laser device 1 shown inFIG. 1 is obtained.

In the quantum cascade laser device 1 described above, thelight-emitting window 11 is joined to the side wall 32 of the package 3by the solder member 16 (in the present embodiment, an SnAgCu-basedsolder material having a melting point of 220° C.) having a lowermelting point than that of a brazing material (melting point is 450° C.or higher). Accordingly, compared to when the brazing material is used,the window member 15 and the counterbore surface 14 can be brought intoclose contact with each other while suppressing damage to the windowmember 15 and the like (particularly, the anti-reflection films 151 and152) caused by heat. In addition, the first region A1 in which theanti-reflection film 151 is provided and the second region A2 to whichthe solder member 16 is joined are separated from each other on theincident surface 15 a of the window member 15 (refer to FIG. 7 ).Accordingly, stress generated in the second region A2 when the soldermember 16 is melted or solidified is prevented from being transmitted tothe anti-reflection film 151 on the first region A1. As a result, damage(crack, peeling, or the like) to the anti-reflection film 151 caused bythe stress is suppressed. As described above, according to the quantumcascade laser device 1, damage to the anti-reflection film 151 providedon the light-emitting window 11 can be suppressed, and high airtightnessof the package 3 can be secured.

In addition, the side surface 15 c of the window member 15 includes thethird region A3 metallized to be continuous with the second region A2,and at least a part of the side surface 15 c is joined to at least apart of the inner surface of the large-diameter hole 13 through thesolder member 16 (refer to FIG. 5 ). According to this configuration,since a region that is continuous from the second region A2 to the sidesurface 15 c of the window member 15 (third region A3) is metallized,when solder joining is performed, some of the solder member 16 suitablywet-spreads to a third region A3 side. As a result, the solder member 16can be interposed between the side surface 15 c of the window member 15and the inner surface of the large-diameter hole 13, and theairtightness of the package 3 can be suitably improved.

In addition, the wavelength of the laser light L emitted from the QCLelement 2 is included within a range of 4 μm to 12 μm. As one example,the heat-resistant temperature of the anti-reflection films 151 and 152is approximately 260° C. On the other hand, in the quantum cascade laserdevice 1, since the solder member 16 having a relatively low meltingpoint is used as a joining material, the window member 15 on which theanti-reflection films 151 and 152 are provided can be attached to theside wall 32 by solder joining while suppressing damage to theanti-reflection films 151 and 152 caused by heat.

In addition, in the quantum cascade laser device 1, the lens holder 9has the small-diameter hole 9 a and the large-diameter hole 9 b of whichthe central axes AX1 and AX2 are eccentric with respect to each other.In addition, the side surface 8 b of the lens 8 is positioned withrespect to the inner surface of the large-diameter hole 9 b along thedirection D from the central axis AX2 of the large-diameter hole 9 btoward the central axis AX1 of the small-diameter hole 9 a. Accordingly,the positional offset of the lens 8 (movement of the lens 8 with respectto the lens holder 9) that may be caused by the surface tension of theresin adhesive agent B1 disposed around the lens 8 in case that the lens8 is disposed at a central portion of the large-diameter hole 9 b (forexample, refer to the left part of FIG. 15 ) can be suitably suppressed.Further, in a state where the lens 8 is positioned in such a manner, thecentral axis AX3 of the lens 8 is disposed at a position close to thecentral axis AX1 of the small-diameter hole 9 a (in the presentembodiment, the central axis AX3 and the central axis AX1 coincide witheach other). Accordingly, the area of a region in which the effectiveregion of the lens 8 (region within the effective diameter around thecentral axis AX3 of the lens) and the counterbore surface 9 c interferewith (overlap) each other can be reduced. As a result, the effectiveregion of the lens 8 can be efficiently used. In addition, since theeffective region of the lens 8 can be efficiently used, the size of thelens 8 can be reduced, and the size of the package 3 can be reduced.

In addition, in the present embodiment, the central axis AX3 of the lens8 substantially coincides with the central axis AX1 of thesmall-diameter hole 9 a, and the effective diameter of the lens 8substantially coincides with the diameter d3 of the small-diameter hole9 a. According to this configuration, the entirety of the effectiveregion (region within the effective diameter) of the lens 8 can beexposed through the small-diameter hole 9 a. Accordingly, the size ofthe small-diameter hole 9 a is suppressed to its minimum to secure thearea of the counterbore surface 9 c, so that it is possible to make themost use of the effective region of the lens 8 while appropriatelysupporting the edge portion of the incident surface 8 a of the lens 8.

In addition, the groove portions 9 d that reach the counterbore surface9 c along the X-axis direction are formed in the inner surface of thelarge-diameter hole 9 b, and the resin adhesive agent B1 enters thegroove portions 9 d. According to this configuration, the resin adhesiveagent B1 can be easily injected into the gap between the side surface 8b of the lens 8 and the inner surface of the large-diameter hole 9 bthrough the groove portions 9 d.

In addition, the lens holder 9 has the lower surface 92 a on which theplurality (in the present embodiment, four) of protrusions 92 bprotruding to the heat spreader 5 side are formed, and the plurality ofprotrusions 92 b are joined to the second upper surface 53 of the heatspreader 5 through the adhesive layer B2 made of a UV curable resin. Inthe present embodiment, the plurality of protrusions 53 a protruding toa lens holder 9 side are formed on the second upper surface 53 at thepositions corresponding to the plurality of protrusions 92 b, and theplurality of protrusions 92 b are joined to the plurality of protrusions53 a through the adhesive layer B2. According to this configuration,since locations where the adhesive layer B2 is provided can be dispersedonto the plurality of protrusions 92 b, the adhesive layer B2 on each ofthe protrusions 92 b can be easily and appropriately cured compared towhen the adhesive layer B2 is provided in a wide range on the entiresurface. Further, in the present embodiment, the adhesive layer B2 isdisposed at a central portion of the space formed between the lowersurface 92 a and the second upper surface 53 (between the protrusions 92b and the protrusions 53 a). Accordingly, the adhesive layer B2 can besuitably irradiated with UV light reflected by the lower surface 92 aand by the second upper surface 53 in the space. As a result, theadhesive layer B2 can be more appropriately cured, and the lens holder 9can be stably fixed to the heat spreader 5.

In addition, the bottom wall portion 92 of the lens holder 9 is providedwith the cutout 92 c for guiding light to the second upper surface 53 ofthe heat spreader 5. According to this configuration, the second uppersurface 53 of the heat spreader 5 can be irradiated with UV light from aside opposite to a side on which the heat spreader 5 is disposed withrespect to the lens holder 9 (namely, from above the lens holder 9),through the cutout 92 c provided in the bottom wall portion 92.Accordingly, light irradiation for curing the adhesive layer B2 betweenthe lower surface 92 a and the second upper surface 53 can be easilyperformed.

In addition, the lens holder 9 includes the top wall portion 91 facingthe bottom wall portion 92 through the large-diameter hole 9 b. Then,the top wall portion 91 is formed not to overlap at least a part of thecutout 92 c provided in the bottom wall portion 92 when viewed in thedirection in which the bottom wall portion 92 and the top wall portion91 face each other (Z-axis direction). According to this configuration,the lens 8 disposed in the large-diameter hole 9 b can be appropriatelyprotected from the outside by the bottom wall portion 92 and the topwall portion 91. In addition, since the top wall portion 91 is formednot to overlap at least a part of the cutout 92 c provided in the bottomwall portion 92, the second upper surface 53 of the heat spreader 5 canbe irradiated with light by irradiating the lens holder 9 with the lightfrom the outside of the lens holder 9 (side opposite to the bottom wallportion 92 with the top wall portion 91 sandwiched therebetween).

In addition, instead of the cutout 92 c, a through-hole penetratingthrough the bottom wall portion 92 in the Z-axis direction may be formedin the bottom wall portion 92. Similarly, instead of the cutout 91 a, athrough-hole penetrating through the top wall portion 91 in the Z-axisdirection and including a portion overlapping the cutout 92 c or thethrough-hole provided in the bottom wall portion 92 may be formed in thetop wall portion 91. Even with such a configuration, light can be guidedto the second upper surface 53 of the heat spreader 5 by performinglight irradiation from above the lens holder 9.

In addition, the QCL element 2 and the lens holder 9 are mounted on thesame heat spreader 5. Incidentally, the QCL element 2 is mounted on theheat spreader 5 with the submount 7 and the heat sink 6 interposedtherebetween. According to this configuration, since a base (heatspreader 5) on which the QCL element 2 and the lens holder 9 are placedis shared, when the heat spreader 5 expands or contracts because ofheat, a relative movement of the lens holder 9 with respect to the QCLelement 2 can be suppressed. As a result, the occurrence of an opticalaxis offset (offset of the central axis AX3 of the lens 8 with respectto the optical axis of the laser light L) caused by a temperature changein the package 3 can be suppressed.

In addition, the package 3 airtightly accommodates the QCL element 2,the lens 8, and the lens holder 9 described above. According to thisconfiguration, since the effective region of the lens 8 disposed in thepackage 3 can be efficiently used, the size of the lens 8 can bereduced, and the size of the package 3 can be reduced.

Modification Examples

One embodiment of the present disclosure has been described above;however, the present disclosure is not limited to the above-describedembodiment. For example, the material and the shape of eachconfiguration are not limited to the material and the shape describedabove, and various materials and shapes can be adopted. In addition,some configurations included in the embodiment may be appropriatelychanged or omitted.

The shape of the lens holder is not limited to the shape of the lensholder 9 described above. For example, instead of the lens holder 9described above, lens holders 9A to 9C shown in FIGS. 17 to 19 may beused.

As shown in FIG. 17 , the lens holder 9A of a first modification examplediffers from the lens holder 9 in that a large-diameter hole 9Ab havinga quadrangular shape is formed instead of the large-diameter hole 9 bhaving a circular shape and the groove portions 9 d are not formed(large-diameter hole 9Ab is formed in such a size as to include portionscorresponding to the groove portions 9 d). In such a manner, thelarge-diameter hole 9Ab may be formed in such a size as to accommodatethe lens 8, and may not necessarily be formed in a circular shape.According to the large-diameter hole 9Ab, a sufficient space for thefilling of the resin adhesive agent B1 can be secured at four corners ofthe large-diameter hole 9Ab without providing the groove portions 9 d.From a different perspective, in the lens holder 9A, each of theportions corresponding to the four corners of the large-diameter hole9Ab functions as a recess corresponding to the groove portion 9 d of thelens holder 9. Incidentally, similarly to the large-diameter hole 9Ab,the small-diameter hole 9 a may also be formed in a shape other than acircular shape (for example, the same quadrangular shape as that of thelarge-diameter hole 9Ab, a size smaller than the large-diameter hole9Ab, or the like).

As shown in FIG. 18 , the lens holder 9B of a second modificationexample differs from the lens holder 9 in that the lens holder 9Bincludes a top wall portion 91B of which an upper surface is formed in acircular shape (curved surface shape), instead of the top wall portion91. In addition, in the lens holder 9B, since the top wall portion 91Bis adopted, there is no space for forming the groove portion 9 dprovided on a top wall portion 91 side in the lens holder 9. For thisreason, in the lens holder 9B, a pair of the groove portions 9 d areformed on both respective sides in the Y-axis direction on a bottom wallportion 92 side. In such a manner, positions where the groove portions 9d are formed in the lens holder are not particularly limited. Inaddition, the number of the groove portions 9 d is not particularlylimited. In addition, in the lens holder 9B, a length of a portion of awall portion along the X-axis direction excluding the bottom wallportion 92 is shorter compared to the wall portion 90 of the lens holder9, the wall portion forming the large-diameter hole 9 b. Specifically,the length of the portion along the X-axis direction is slightly shorterthan a length of the lens 8 along the X-axis direction. According tosuch a configuration, since a portion that blocks UV light from abovethe lens holder 9B can be reduced, the UV light for curing the adhesivelayer B2 can be more suitably guided to the heat spreader 5 side.

As shown in FIG. 19 , the lens holder 9C of a third modification examplediffers from the lens holder 9 in that the lens holder 9C includes a topwall portion 91C having a shorter length along the X-axis direction thanthat of the top wall portion 91, instead of the top wall portion 91. Thelength of the top wall portion 91C along the X-axis direction isapproximately half the length of the lens 8 along the X-axis direction.In addition, in the lens holder 9C, a length of a portion of a wallportion along the X-axis direction excluding the bottom wall portion 92is the same as that of the top wall portion 91C, the wall portionforming the large-diameter hole 9 b. Namely, the lens holder 9C isformed in a substantially L shape when viewed in the Y-axis direction.In the lens holder 9C, since a portion that blocks UV light from abovethe lens holder 9C is smaller than in the lens holder 9B, the UV lightfor curing the adhesive layer B2 can be more suitably guided to the heatspreader 5 side. In addition, as in the lens holder 9C, the wall portionof the lens holder forming the large-diameter hole 9 b does not need tosurround the entirety of the side surface 8 b of the lens 8, and may beconfigured to surround only a part of an incident surface 8 a side ofthe side surface 8 b of the lens 8.

In addition, as in a quantum cascade laser device 1A according to amodification example shown in FIG. 20 , the lens may not necessarily beaccommodated in the package 3. The quantum cascade laser device 1Adiffers from the quantum cascade laser device 1 in that the quantumcascade laser device 1A includes a lens 8A externally attached to anouter side of the package 3, instead of including the lens 8 and thelens holder 9 in the package 3. Namely, the quantum cascade laser device1A includes the lens 8A disposed on the outer side of the package 3 toconcentrate or collimate the laser light L that has transmitted throughthe light-emitting window 11. In addition, because of the difference,the quantum cascade laser device 1A differs from the quantum cascadelaser device 1, also in that the quantum cascade laser device 1Aincludes a heat spreader 5A configured such that the QCL element 2 canbe disposed at a position close to the light-emitting window 11, insteadof the heat spreader 5. As described above, the beam radiation angle ofthe laser light L is very large. For this reason, in order to make thelight-emitting window 11 as small as possible while allowing all lightfluxes of the laser light L to pass through the light-emitting window 11to the outside of the package 3, it is desirable that the light-emittingwindow 11 and the emitting surface (end surface 2 a) of the QCL element2 that emits the laser light L are brought as close as possible to eachother. For this reason, the quantum cascade laser device 1A notincluding the lens inside the package 3 includes the heat spreader 5Adescribed above.

According to the quantum cascade laser device 1A, since the lens 8A is amember to be externally attached that is disposed on the outer side ofthe package 3, the disposition, replacement, and the like of the lens 8can be flexibly performed. Further, as described above, the length w1 ofthe small-diameter hole 12 along the optical axis direction (X-axisdirection) of the laser light L is shorter than the length w2 of thelarge-diameter hole 13 (refer to FIG. 5 ). According to thisconfiguration, the light-emitting window 11 can be brought closer to theQCL element 2 compared to when the length w1 of the small-diameter hole12 is equal to or longer than the length w2 of the large-diameter hole13. Accordingly, even when the beam radiation angle of the laser light Lemitted from the QCL element 2 is large, the laser light L can beincident on the light-emitting window 11 while a degree of the spread ofthe laser light L is reduced. As a result, the size of thelight-emitting window 11 can be reduced, and the size of the package 3can be reduced.

In addition, as described above, the emitting surface 15 b of the windowmember 15 includes the fourth region A4 in which the anti-reflectionfilm 152 is provided, and the fourth region A4 includes the first regionA1 and is larger than the first region A1 when viewed in the X-axisdirection. As in the quantum cascade laser device 1A, when the lens isnot provided in the package 3 and the laser light L that is divergentlight is incident on the window member 15, a region through which thelaser light L passes on the incident surface 15 a of the window member15 is smaller than a region through which the laser light L passes onthe emitting surface 15 b of the window member 15. Therefore, as in thisconfiguration, a region corresponding to a difference between the fourthregion A4 and the first region A1 can be secured as the second region A2by making the anti-reflection film 151 on an incident surface 15 a sidesmaller than the anti-reflection film 152 on an emitting surface 15 bside (namely, by making the first region A1 smaller than the fourthregion A4). In such a manner, since the sizes of the first region A1,the second region A2, and the fourth region A4 are designed inconsideration of the beam radiation angle of the laser light L, the sizeof the window member 15 can be reduced, and the size of the package 3can be reduced.

In addition, in the embodiment, the emitting surface 15 b of the windowmember 15 is substantially flush with the outer surface of the side wall32, but the emitting surface 15 b of the window member 15 may furtherprotrude to the outside of the package 3 than the outer surface of theside wall 32. Namely, the thickness of the window member 15 may belarger than the length w2 of the large-diameter hole 13. In this case,the workability when the window member 15 is joined to the side wall 32from the outside of the package 3 can be improved. In addition, as inthe quantum cascade laser device 1A, when the lens 8A to be externallyattached is attached to the emitting surface 15 b of the window member15, the workability of lens attachment can also be improved. Inaddition, the size of the package 3 can be reduced or the lens 8A can bereliably disposed close to the window member 15 by reducing thethickness of the side wall 32.

In addition, in the embodiment, as one example of the semiconductorlaser element, the quantum cascade laser element (QCL element 2) hasbeen exemplified, but as the semiconductor laser element to beaccommodated in the package 3, a laser element other than the quantumcascade laser element may be used. In addition, the semiconductor laserelement may be a distributed feedback (DFB) semiconductor laser elementin which a diffraction grating structure is provided on an upper portionof an active layer.

In addition, in the embodiment, the package 3 that is a butterflypackage has been exemplified, but the form of the package is not limitedthereto. For example, the package may be a CAN package.

REFERENCE SIGNS LIST

1, 1A: quantum cascade laser device (semiconductor laser device), 2:quantum cascade laser element (semiconductor laser element), 2 a: endsurface (emitting surface), 3: package, 5, 5A: heat spreader, 8, 8A:lens, 8 a: incident surface, 8 b: side surface, 8 c: emitting surface,9, 9A, 9B, 9C: lens holder, 9 a: small-diameter hole (first holeportion), 9 b: large-diameter hole (second hole portion), 9 c:counterbore surface, 9 d: groove portion (recess), 11: light-emittingwindow, 12: small-diameter hole, 13: large-diameter hole, 14:counterbore surface, 15: window member, 15 a: incident surface, 15 b:emitting surface, 15 c: side surface, 16: solder member, 31: bottomwall, 32: side wall, 33: top wall, 53: second upper surface (secondattachment surface), 53 a: protrusion (second protrusion), 91: top wallportion (second wall portion), 92: bottom wall portion (first wallportion), 92 a: lower surface (first attachment surface), 92 b:protrusion (first protrusion), 92 c: cutout, 151: anti-reflection film(first anti-reflection film), 152: anti-reflection film (secondanti-reflection film), 153: metal film, A1: first region, A2: secondregion, A3: third region, A4: fourth region, AX1, AX2, AX3: centralaxis, B1: resin adhesive agent, B2: adhesive layer, D: direction, L:laser light.

1: A quantum cascade laser device comprising: a quantum cascade laserelement; a lens disposed to face an emitting surface of the quantumcascade laser element that emits laser light; and a lens holder thatholds the lens, wherein the lens holder includes: a first hole portionextending in an optical axis direction along an optical axis of thelaser light; a second hole portion that is provided at a positionfarther from the quantum cascade laser element than the first holeportion, and that includes the first hole portion and is larger than thefirst hole portion when viewed in the optical axis direction; and acounterbore surface having an annular shape that connects the first holeportion and the second hole portion and that extends along a planeintersecting the optical axis direction, the lens includes: an incidentsurface on which the laser light is incident; and a side surfaceextending from an edge portion of the incident surface along the opticalaxis direction, at least a part of the side surface is fixed to an innersurface of the second hole portion through a resin adhesive agent in astate where the edge portion of the incident surface is in contact withthe counterbore surface, a central axis of the first hole portion iseccentric from a central axis of the second hole portion, the sidesurface of the lens is positioned with respect to the inner surface ofthe second hole portion along a direction from the central axis of thesecond hole portion toward the central axis of the first hole portion,and a central axis of the lens is disposed at a position closer to thecentral axis of the first hole portion than to the central axis of thesecond hole portion. 2: The quantum cascade laser device according toclaim 1, wherein the central axis of the lens substantially coincideswith the central axis of the first hole portion, and an effectivediameter of the lens substantially coincides with a diameter of thefirst hole portion. 3: The quantum cascade laser device according toclaim 1, wherein a recess that reaches the counterbore surface along theoptical axis direction is formed in the inner surface of the second holeportion, and the resin adhesive agent enters the recess. 4: The quantumcascade laser device according to claim 1, further comprising: a heatspreader on which the lens holder is mounted, wherein the lens holderincludes a first attachment surface on which a plurality of firstprotrusions protruding to a heat spreader side are formed, and theplurality of first protrusions are joined to a second attachment surfaceof the heat spreader through an adhesive layer made of a photocurableresin. 5: The quantum cascade laser device according to claim 4, whereina plurality of second protrusions protruding to a lens holder side areformed on the second attachment surface at positions corresponding tothe plurality of first protrusions, and the plurality of firstprotrusions are joined to the plurality of second protrusions throughthe adhesive layer. 6: The quantum cascade laser device according toclaim 4, wherein a first wall portion having the first attachmentsurface of the lens holder is provided with a through-hole or a cutoutfor guiding light to the second attachment surface of the heat spreader.7: The quantum cascade laser device according to claim 6, wherein thelens holder includes a second wall portion facing the first wall portionthrough the second hole portion, and the second wall portion is formednot to overlap at least a part of the through-hole or the cutoutprovided in the first wall portion, when viewed in a direction in whichthe first wall portion and the second wall portion face each other. 8:The quantum cascade laser device according to claim 1, wherein thequantum cascade laser element and the lens holder are mounted on a sameheat spreader. 9: The quantum cascade laser device according to claim 1,further comprising: a package that airtightly accommodates the quantumcascade laser element, the lens, and the lens holder, wherein thepackage includes: a bottom wall; a side wall standing on the bottom walland being formed in an annular shape to surround a region in which thequantum cascade laser element and the lens holder are accommodated, whenviewed in a direction perpendicular to the bottom wall; and a top wallthat closes an opening on an opposite side of the side wall from abottom wall side, and a light-emitting window through which the laserlight that has passed through the lens passes is provided on the sidewall.